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Li Jingling; Top-down and bottom-up controls in visual search: Evidence from a large task-irrelevant salient distracter. Journal of Vision 2010;10(7):1282. doi: 10.1167/10.7.1282.
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In this study we explore how a salient line irrelevant to the task affects visual search. The search display was a lattice of regularly spaced short horizontal bars covering the entire screen. The target was a small oriented gap in one of the bars, always located on the same horizontal line in the middle of the display. The task was to discriminate a leftward vs. rightward slant of the gap. The salient line was formed by rotating the texture bars in one vertical column by 90 deg. It thus was orthogonal to the texture. The location of the target and salient line varied independently from trial to trial. Therefore the salient line did not predict target location. Reaction time was used as a dependent variable. In Experiment 1, a target presented directly on the salient line was discriminated less quickly and less reliably, suggesting that the salient line impaired visual search. In Experiment 2, the impairment caused by the salient line became progressively less by decreasing the line length. The impairment persisted, however, even when the salient line was shortened to a single vertical bar. In Experiment 3, the salient line continued to impair visual search despite extensive practice. In Experiment 4, the salient line actually facilitated visual search when it was defined by color, rather than orientation. Both the length and practice effect suggest that the search was, in part, under bottom-up control, whereas the facilitation due to color suggests a top-down effect on target detection.
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